1. Field of the Invention
This invention relates to an apparatus and method for introducing liquid crystal into liquid crystal cells and, more particularly, to an apparatus and method which permit introduction of an adequate amount of liquid crystal into liquid cells efficiently and automatically.
2. Description of the Prior Art
A liquid crystal cell of a liquid crystal display is fabricated by sealing liquid crystal in a cell which comprises two, slightly spaced-apart glass plates facing each other. The cell has a transparent electrode formed on the inner surface of each of the two glass plates. When the transparent electrodes are energized, a display is provided on it according to the pattern of the electrodes.
FIG. 9 shows such a liquid crystal cell 1. As shown in the Figure, two glass plates 2 are bonded together by an adhesive spacer 3 which is coated such as to enclose a display area and separate the glass plates 2 by a predetermined minute distance.
The cell thus has an inner space defined by the two glass plates and the adhesive spacer intervening therebetween in a dam-like fashion such as to enclose the display area. Liquid crystal is sealed in this cell. To seal liquid crystal, the adhesive spacer intervening in the dam-like fashion between the two glass plates has a gap 5, which serves as an inlet 6 for introducing liquid crystal therethrough.
To seal liquid crystal in the entire inner space of the cells 4 having the above structure, liquid crystal is introduced in the following way.
A plurality of cells 4 are held with their liquid crystal inlet 6 directed downward on a magazine or like holding means 7, which is disposed in a vacuum vessel (not shown). The vacuum vessel is then evacuated to sufficiently purge the air in each of the cells 4. Then, the inlet 6 of each cells 4 is brought into contact with the surface of liquid crystal provided in a lower liquid crystal boat This may be effected by lowering the magazine 7. To save as much liquid crystal as possible, attached to the lower edge of each cell 4, the liquid crystal boat has a structure like a narrow groove so that the liquid crystal provided therein has a convex surface owing to its surface tension.
With the inlet of the cell held in contact with and closed by the liquid crystal surface in the above way, the pressure in the vacuum vessel is then increased. By so doing, the liquid crystal is introduced through the inlet into the inner space of the cell with increase of the external pressure.
Thereafter, the cell containing the introduced liquid crystal is taken out of the vacuum vessel, and liquid crystal attached to the cell lower edge is removed by wiping, for instance. The inlet is then sealed using an ultraviolet-ray-setting resin or like sealing material.
The above method of sealing liquid crystal has the following problems.
Firstly, the formation of the convex liquid crystal surface on the liquid crystal boat by utilizing the surface tension is very difficult to control. Inadequate control may result in that a large amount of liquid crystal is spilled when the cell inlet contacts the liquid surface, and that air bubbles are introduced into the cell when the inner pressure of the vacuum vessel is increased. To preclude the generation of such air bubbles, one must hold the liquid crystal surface at a predetermined convex shape by utilizing the surface tension, but it is a delicate control and very difficult.
As a second problem, the liquid crystal boat 8 has a structure like a narrow groove, and its volume is comparatively small. Therefore, for controlling the liquid crystal surface control it is necessary to replenish the liquid crystal boat for every liquid crystal introduction by reducing and then increasing the vacuum vessel pressure. Such replenishing operation is again very cumbersome.
As a third problem, even if liquid crystal could be successfully introduced in a predetermined amount in the cell, it is introduced by holding the inlet of the cell in contact with and closed by its surface. Therefore, even by minimizing the contact area of the cell lower edge with the inlet by forming the convex liquid crystal surface by utilizing the surface tension thereof, excess liquid crystal is more or less attached to the cell when the cell is separated from the liquid crystal surface after introduction of liquid crystal. Although such excess liquid attached to one cell is slight in amount, it amounts to be considerable with repeated liquid crystal introduction operations carried out for a large number of cells. Such excess crystal liquid is only removed by wiping or the like and can not be used again. This means a great loss of liquid crystal.
FIG. 8 shows a measure to solve the above problems posed when sealing liquid crystal by using the liquid crystal boat having a structure like a narrow groove, that is, the difficulty of the liquid crystal surface control and the cumbersome replenishment of liquid crystal. In this case, the lower edge of cell vessels is dipped in a comparatively large amount of liquid crystal contained in a liquid crystal trough 9. In this case, however, a large amount of liquid crystal is attached not only to the lower edge of each cell but also to the magazine holding the cells, thus resulting in great loss of liquid crystal. Currently, therefore, this method is unfeasible.
An object of the invention, accordingly, is to provide an apparatus and a method for introducing liquid crystal into liquid crystal cells, which permit reliable introduction of a proper amount of liquid crystal into each liquid crystal cell with a simple operation and without loss of liquid crystal.